1. Field of the Invention
This invention relates generally to cement compositions including mixtures of substantially elastic material and cement and, in one application, to methods for cementing using such cement compositions in substantially closed systems, such as the interior of a mold used for producing preformed concrete items.
2. Description of the Related Art
Cement inflatable packers were originally developed to provide isolation in open holes for stimulation treatments and for water shutoff. Today these packers are being used as an integral part of completion operations to, among other things, provide zonal isolation, control gas migration, isolating the junctions of multilateral completions, and for gravel packing. However, the success rate associated with inflatable packer completions has typically been low. This low success rate has been attributed to, among other things, volumetric shrinkage of Portland cement which is typically employed to inflate cement inflatable packers.
A typical inflatable packer has an annular elastomer packer element mounted around a central tubular member. The elastomer packer element is adapted to receive cement slurry or other fluid, such as drilling mud, under pressure in such a way that the packer element is inflated and compressed between the inflation liquid and the wall of a wellbore. During use, such an inflatable packer is typically run into a wellbore on a pipe string and positioned at a selected setting depth within the wellbore. Once inflated by an inflation fluid, such as cement, a valve system is typically provided within the packer in order to isolate the inflation fluid under pressure inside the inflated elastomer packer element. When used to achieve zonal isolation, the trapped inflating pressure of the inflation fluid within the elastomer packer element must be sufficiently high to maintain a positive hydraulic seal between the exterior of the packer element and the borehole wall.
In typical completion operations, Portland cement is used to inflate the element of an inflatable packer. Typically, a Portland cement undergoes a reduction in volume of from about 2% to about 4.5% during curing or hydration. In well cementing applications not involving inflatable packers, this volume loss is often masked or compensated for by the fact that free water, available from subterranean formations, imbibes into the exposed setting cement. This offsets shrinkage and may even cause a slight expansion. However, in a substantially closed system, such as that present within an inflatable packer, this osmotic transfer of water does not occur. As a consequence, shrinkage and dimensional changes of conventional Portland cement upon curing within an elastomer packer element may result in lack of sufficient pressure or strain to maintain a positive seal. This may result in the formation of a microannulus or other zone of communication which permits pressure and/or fluid communication across one or more areas between the inflated packer element and the borehole wall. Therefore, cement dimensional changes within an inflatable packer have often been linked to various completion problems, including interzonal communication and migration of fluids, such as gas. Such problems typically require costly remedial efforts which may or may not be successful.
Other applications in which cement shrinkage and dimensional changes may have adverse effects include cement applications in other substantially closed systems, such as during annular cementing of concentric strings of pipe in a wellbore. Such adverse effects may also result in the formation of a zone of communication which permits pressure and/or fluid communication across one or more areas in the annular space between the strings of pipe, resulting in various completion problems, including interzonal communication and fluid migration. Substantially closed systems and problems associated therewith may also be present in non-wellbore cementing applications as well.
In an effort to control or prevent cement shrinkage, additives have been developed which favor the expansion of cement. Such additives include materials such as salt, hemihydrated calcium sulfate, magnesium (calcium) oxide, and mixtures thereof. These additives typically require an extraneous source of water to effect expansion of the set cement. Therefore, even with these additives, most cement slurries will exhibit shrinkage under conditions where no access to external water is provided, such as those conditions found within an inflatable packer element. Magnesium oxide and magnesium (calcium) oxide additives used in sufficient concentrations with conventional cements may cause expansion without access to external water, but typically produce excess surface mixing viscosities, are difficult to retard under downhole conditions, and may deteriorate (i.e., exhibit cracking, excessive porosity, etc.) due to excessive increases in bulk volume, and/or uncontrolled expansion.
In an attempt to compensate for the lack of external water available to cement in a closed system, greater amounts of expanding agents (typically greater than 10% by weight) have been employed. However, a number of disadvantages are associated with these relatively high levels of expanding agent concentrations. Such disadvantages include shortened thickening times, excessive mixing viscosity, placement problems, downhole rheologies that create high friction during placement, and high cost. Gas generating additives may be employed to impart expansion, however these materials typically generate flammable gases. The effect of such gases on the long term stability of metal and/or sealing elements is unknown.
Disclosed herein are compositions and methods of cementing therewith. In one embodiment, a composition may include a mixture of hydraulic cement and a substantially elastic material, and a method of cementing may include placing an uncured cement composition in a selected location and allowing the cement composition to cure to form a cured cement composition; wherein the uncured cement composition includes a mixture of hydraulic cement and substantially elastic material. The substantially elastic material may be selected so that at least a portion of the substantially elastic material yields (i.e., deforms or compresses to a volume that is smaller than the volume of the elastic material in its non-compressed state) under conditions existing when the uncured cement composition is placed in the selected location. Such conditions may include, for example, exposure to pressure or other compressional forces present in the selected location when the uncured cement is placed in position. In one embodiment, the cured cement composition may be formulated to exhibit substantially the same to bulk volume upon curing in the absence of external water as the bulk volume of the uncured cement composition (or to exhibit a net shrinkage in bulk volume upon curing in the absence of external water of less than about 1% as compared to the bulk volume of the uncured cement composition).
In another respect, disclosed is a method of cementing within a wellbore, including introducing an uncured cement slurry into a wellbore, and allowing the cement slurry to cure to form a cured cement composition. In this method the uncured cement slurry may include a mixture of hydraulic cement and a particulate material, with the particulate material being substantially elastic under in situ cementing conditions. Furthermore, within the wellbore, at least a portion of the individual particles of the substantially elastic particulate material may each have a respective first volume at in situ wellbore cementing conditions prior to curing of the cement slurry; and may also each have a respective second volume at in situ wellbore cementing conditions after curing of the cement slurry to form the cured cement composition, with the second volume being larger than the first volume so as to at least partially counteract volumetric shrinkage of the cement slurry during curing.
In another respect, disclosed is a method of placing a cement composition within a substantially closed system (such as placing cement in an annular space existing between two concentric strings of pipe in a subterranean wellbore, or inflating an inflatable packer positioned within a subterranean wellbore). The method may include the step of introducing into the substantially closed system an uncured cement composition which includes a mixture of substantially elastic material (such as substantially elastic particulate material) and cement In one embodiment, individual particles of a substantially elastic material may have any size, shape, and/or configuration suitable for admixture and displacement with a cement composition, so that when present in an effective amount in the cement composition it is capable of exerting resilient or elastic force so as to be effective to at least partially counteract volumetric shrinkage of the cement composition during curing (e.g., by exerting resilient or elastic force in opposition to pressure or compressional forces existing within an inflatable packer). Advantageously, such substantially elastic particles may act to minimize shrinkage of cement upon curing by at least partially xe2x80x9creboundingxe2x80x9d from a compressed or deformed shape induced by exposure of the elastic particles to pressure or other compressional forces present when the uncured cement is placed in position. Such rebounding may occur, due to the resilient or elastic force exerted by the substantially elastic material as pressure or other compressional forces decrease during curing of the cement (e.g., as may occur within a substantially closed system such as an inflatable packer)
In another respect, disclosed is a method of placing a cement composition within a substantially closed system, including the step of introducing into the substantially closed system a cement composition which includes a mixture of substantially elastic particulate material and cement. In this method, an effective amount of substantially elastic particulate material may be present in the composition so that the volume of cement composition including the substantially elastic particles and cement advantageously exhibits a volumetric shrinkage (i.e., final volume of cured cement relative to initial volume of uncured cement within the substantially closed system) during cement curing that is less than the volumetric shrinkage exhibited by a cement composition including the cement alone during cement curing.
In another respect, disclosed is a method of placing a cement composition within a substantially closed system, including the step of introducing into the substantially closed system a cement composition which includes a blend or mixture of substantially elastic particulate material and cement, the mixture may include between about 1% to about 50% substantially elastic particulate material by weight, alternatively from about 10% to about 40% substantially elastic particulate material, alternatively from about 10% to about 30% substantially elastic particulate material, alternatively from about 10% to about 20% substantially elastic particulate material, alternatively from about 20% to about 30% substantially elastic particulate material by weight of total weight of the cement composition. In one embodiment, at least a portion of the individual particles of the substantially elastic particulate material may include two or more components. In another embodiment, at least a portion of the individual particles of the substantially elastic particulate material may have a shape with a maximum length-based aspect ratio of equal to or less than about 5. In yet another embodiment, the substantially elastic particulate material may be substantially solid in structure, meaning that individual particles of a substantially elastic material have a structural matrix that is substantially uniform in physical composition and that contains substantially no micro structure and/or porosity. Where substantially no measurable porosity is present, a substantially elastic material may be characterized as being xe2x80x9csubstantially non-porous.xe2x80x9d
In another respect, disclosed is a method of placing a cement composition within a substantially closed system, including the step of introducing into the substantially closed system a cement composition which includes a mixture of substantially elastic particulate material and cement, wherein at least a portion of the individual particles of the substantially elastic particulate material include an agglomerate of substantially non-elastic material and one or more substantially elastic materials, a core of substantially non-elastic material surrounded by one or more layers of substantially elastic material, or a mixture thereof, and wherein the substantially elastic particulate material is capable of at least partially recovering size and/or shape after deformation caused by exposure to an external force, such as pressure or compressional forces, as described in further detail herein. The substantially elastic particulate material may be present in an amount effective to achieve one or more of the cement composition characteristics described elsewhere herein.
In another respect, disclosed is a method for inflating an inflatable packer coupled to a pipe suspended within a subterranean wellbore, and having at least one elastomeric packer element with an inner surface disposed in fluid communication with the string of pipe. The packer may be so inflated, for example, to obtain zonal isolation. The method may include expanding the packer element with an uncured cement slurry by pumping the uncured cement slurry down the string of pipe and into the packer element, and allowing the uncured cement slurry to cure within the expanded packer element to form a cured cement composition. The uncured cement slurry may include a mixture of hydraulic cement and a particulate material, the particulate material being substantially elastic under in situ cementing conditions; and the substantially elastic particulate material may be present in the uncured cement slurry in an amount effective to at least partially counteract volumetric shrinkage of the cement slurry during curing. In one embodiment, the packer element may be expanded sufficiently to form a positive seal between the packer element and a wall of the wellbore, and the uncured cement slurry allowed to cure so that the positive seal is maintained between the packer element and the wellbore wall after the cement slurry has cured to form the cured cement composition. The positive seal may advantageously be effective to substantially prevent gas migration and/or may advantageously be effective to substantially prevent a microannulus from existing between the packer element and the wellbore wall.
In another respect, disclosed is a method of inflating an inflatable packer positioned within a subterranean wellbore including the step of inflating the packer with an inflation fluid or cement composition which includes a mixture of substantially elastic particles or substantially elastic particulate material and cement. In this method, substantially elastic particulate material may be present in an amount effective to cause the pressure exerted on the elements of the inflatable packer by the cement composition including the substantially elastic particles during cement curing to be advantageously greater than the pressure exerted on the elements of the inflatable packer by an inflation fluid including the cement alone (i.e., without the effective amount of substantially elastic particulate material) during cement curing.
In another respect, disclosed is a cement composition that includes a mixture of substantially elastic particulate material and cement. In one embodiment, the cement composition may be a dry cement composition, including a mixture of hydraulic cement and substantially elastic material. In another embodiment, at least a portion of the individual particles of the substantially elastic particulate material may include a core of substantially non-elastic material surrounded by one or more layers of substantially elastic material. In another embodiment, the substantially elastic material may have a maximum length-based aspect ratio of equal to or less than about 5.
In another respect, disclosed herein are individual particles of substantially elastic particulate material that may be combined with hydraulic cement. The particles may have a shape with a maximum length-based aspect ratio of equal to or less than about 5. Such individual particles of substantially elastic particulate material may also have a shape that is at least one of beaded, cubic, bar-shaped, cylindrical, or a mixture thereof. In this regard, beaded or cylindrical shaped particulate materials may have a length to diameter aspect ratio of equal to or less than about 5, and bar-shaped particulate material may have a length to width aspect ratio of equal to or less than about 5 and a length to thickness aspect ratio of equal to or less than about 5. However, it will be understood with benefit of this disclosure that the above aspect ratios are exemplary only, and that in other embodiments, maximum length-based aspect ratio, as well as length to diameter, length to width, and/or length to thickness aspect ratios may be greater than about 5.
In another respect, disclosed herein are individual particles of substantially elastic particulate material that may be combined with hydraulic cement, and that may have a particle size of from about 4 mesh to about 500 mesh, a specific gravity of from about 0.4 to about 3.5, and a shape with a maximum length-based aspect ratio of equal to or less than about 5.
In another respect, disclosed herein are individual particles of substantially elastic particulate material that may be combined with hydraulic cement, and that may be included of a copolymer, such as a terpolymer, which may be at least one of polystyrene/vinyldivinyl benzene, acrylate-based terpolymer or a mixture thereof. For example, substantially elastic material may also be polystyrene divinylbenzene that includes from about 0.5% to about 14% divinylbenzene by weight.
In another respect, disclosed herein are individual particles of substantially elastic particulate material that may be combined with hydraulic cement, and in which at least a portion of the individual particles of the substantially elastic material may include two components such as, for example, a core of substantially non-elastic material surrounded by a layer of substantially elastic material. In this regard, the core may include a material selected from at least one of silica, ceramics, synthetic organic particles, glass microspheres, or a mixture thereof; and the layer of substantially elastic material may include at least one of a cross-linked polymer, plastic, or a mixture thereof. Alternatively, the core may include a material selected from at least one of silica, ceramics, synthetic organic particles, glass microspheres, or a mixture thereof; the layer of substantially elastic material may include resin and make up greater than 8% by weight of the total weight of the particle. A substantially elastic particle may also be an agglomerate of substantially non-elastic material and substantially elastic material with the substantially elastic material making up between about 5% and about 50% by volume of the total volume of each of the individual particles of the material; and the substantially non-elastic material making up between about 50% and about 95% by volume of the total volume of each of the individual particles of the material. Alternatively, a substantially elastic particle may include at least one of a core component of a first material surrounded by at least one layer component of second material, or may include a first material impregnated with a second material, or may include a mixture thereof; wherein in any of these cases the first material of the particles may include at least one of ground or crushed nut shells, ground or crushed seed shells, ground or crushed fruit pits, processed wood, or a mixture thereof; and the second material may include a substantially elastic material as further described herein.